This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-153383, filed May 24, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a cathode ray tube apparatus, particularly, to a cathode ray tube apparatus equipped with a deflection yoke having horizontal and vertical deflection coils.
In general, a cathode ray tube apparatus comprises a vacuum envelope including a substantially rectangular panel, a funnel contiguous to the panel, and a cylindrical neck contiguous to the small diameter portion of the funnel. A phosphor screen including a plurality of phosphor layers emitting red, green and blue lights and a light shielding layer is formed on the inner surface of the panel. A deflection yoke is mounted to the outer circumferential surface ranging from the neck to the funnel, and an electron gun assembly emitting three electron beams corresponding to the colors of the emitted lights on the phosphor screen is arranged within the neck.
A shadow mask performing the color selecting function is arranged inside the panel between the electron gun assembly and the phosphor screen so as to shape the electron beam emitted from the electron gun assembly and to project the shaped electron beam as a beam spot on the phosphor layer with a predetermined color.
The deflection yoke includes horizontal deflection coils for deflecting in a direction of the horizontal axis the three electron beams emitted from the electron gun assembly in the direction of the tube axis and vertical deflection coils for deflecting the three electron beams in a direction of the vertical axis perpendicular to the tube axis and the horizontal axis. In a high precision color cathode ray tube apparatus achieved in recent years, the horizontal deflection coils comprise two saddle type coils opposing to each other with interposing the horizontal axis therebetween and connected in parallel to each other. Likewise, the vertical deflection coils comprise two saddle type coils arranged in series with the vertical axis interposed therebetween.
In the color cathode ray tube apparatus of the construction described above, the horizontal deflection coils are driven by a high voltage pulse, with the result that, under certain conditions, vibration of an electric energy takes place immediately after the fall of the pulse voltage. It should be noted that the vibration of the electric energy causes the horizontal deflection current to be vibrated. As a result, a ringing, i.e., occurrence of bright-dark stripes, is generated immediately after initiation of the image scanning so as to deteriorate the image quality.
Measures for suppressing the ringing problem in the case where the ringing is caused by the deflection yoke are proposed in, for example, Japanese Patent Disclosure (Kokai) No. 61-104544 and Japanese Utility Model Disclosure No. 3-39969. Specifically, disclosed in each of these prior arts is a cathode ray tube in which one portion of the horizontal deflection coil or the vertical deflection coil is connected to another circuit portion via a resistor and a capacitor. To be more specific, Japanese Patent Disclosure No. 61-104544 teaches that a terminal is arranged in the intermediate portion of the winding of each of a pair of horizontal deflection coils that are connected in parallel. In this case, in one of the horizontal deflection coils, the terminal in the intermediate portion is connected to a high potential side with a capacitor interposed therebetween. On the other hand, in the other horizontal deflection coil, the terminal in the intermediate portion is connected to a low potential side with another capacitor interposed therebetween. It is taught that the particular construction permits changing the circuit constant so as to suppress the ringing problem.
However, where a capacitor or the like is connected to the horizontal deflection coil as proposed in Japanese Patent Disclosure NO. 61-104544, the capacitor, etc. is connected to a high potential portion having a potential of several hundred volts to 1.5 kV. It follows that a difficulty in terms of the manufacturing cost must be overcome for achieving the particular construction proposed in this prior art while ensuring a sufficient reliability in respect of the safety.
To be more specific, it is necessary to increase the size of the capacitor in order to ensure a breakdown voltage of the capacitor. Also, when it comes to the wiring, it is necessary to increase the size of the wiring substrate in order to ensure a sufficient insulating distance from the low potential portion, leading to an increase in the manufacturing cost.
The present invention has been contrived in consideration of the above circumstances, and its object is to provide a cathode ray tube apparatus capable of suppressing the ringing problem with a high safety and at a low cost.
In order to achieve the above noted object, a cathode ray tube apparatus according to the present invention comprises a vacuum envelope including a panel having a phosphor screen formed on an inner surface thereof, and a funnel contiguous to the panel; an electron gun assembly arranged within a neck of the vacuum envelope, for emitting electron beams toward the phosphor screen; and a deflection yoke mounted on the outer circumferential surface of the neck and the funnel.
Where the vacuum envelope has a tube axis, a first axis perpendicular to the tube axis, and a second axis perpendicular to both the tube axis and the first axis, the deflection yoke includes a pair of horizontal deflection coils arranged to face each other with the first axis interposed therebetween and extending in the direction of the tube axis, for deflecting and scanning the electron beams in the direction of the first axis, and a pair of vertical deflection coils arranged to face each other with the second axis interposed therebetween and extending in the direction of the tube axis, for deflecting and scanning the electron beam in the direction of the second axis.
Each of the horizontal deflection coil and the vertical deflection coil has the distribution of the winding within an angular region sandwiched between the first axis and the second axis in a cross section including both the first axis and the second axis, the winding of each horizontal deflection coil is mainly distributed in an angular region close to the first axis, and the winding of each vertical deflection coil is mainly distributed in an angular region close to the second axis.
The pair of horizontal deflection coils are connected in parallel to each other.
Each of the horizontal deflection coils has a relatively high potential on the side of the first axis and a relatively low potential on the side of the second axis, and includes a first terminal positioned on the side of a relative high potential, a second terminal positioned on the side of a relatively low potential, and a third terminal positioned in the intermediate portion of the winding and formed on the side of a low potential relative to a portion where the inductance of the horizontal deflection coil is equally divided into two halves.
Further, a capacitor is connected between the third terminal of each of the horizontal deflection coils and the second terminal on the side of the low potential compared with the third potential or the ground potential point.
The present invention also provides a cathode ray tube apparatus, which is featured in that the third terminal of each of the horizontal deflection coils is formed on the side of the second axis, compared with the distribution angle of the winding distribution of the vertical deflection coil at the edge on the side of the first axis.
As described previously, the ringing phenomenon is caused by various factors. In general, the vibration energy of the ringing phenomenon is imparted by the horizontal deflection pulse. Where the ringing phenomenon is caused by the deflection yoke, it is considered reasonable to understand that the ringing phenomenon is caused by the resonance phenomenon between the inductance of the deflection coil and the distributed capacitance present around the deflection coil. The vibration frequency f of the vibration energy is represented by the formula given below and, thus, is determined by the inductance L and the capacitance C:
f=2xcfx80{square root over (1/LC)}
The inductance L is unavoidable because the inductance L is present as the deflection coil itself. The distributed capacitance C is also unavoidable because the distributed capacitance C is spontaneously generated if a potential difference is generated between two insulated conductors.
According to the cathode ray tube apparatus of the construction described above, the high potential side of each of the horizontal deflection coils is on the side of the first axis, and the second axis side close to the vertical deflection coil constitutes a low potential side. In order to suppress the vibration of the ringing caused by the coupling between the horizontal deflection coil and the vertical deflection coil, a third terminal is formed in the vicinity of the center of the winding of each of the horizontal deflection coils. It should be noted that a capacitor is connected between the third terminal and the second terminal on the side of the low potential such that the vibration generated by the distributed capacitance on the side of the second axis is suppressed by changing the resonance condition.
It should also be noted that the ringing generation is caused in that portion of each of the horizontal deflection coils which is positioned close to the vertical deflection coil. It is possible to lower the breakdown voltage of the capacitor by allowing the particular portion of the horizontal coil noted above to bear a low potential so as to lower the manufacturing cost. Also, since the third terminal is formed on the low potential side relative to the portion where the inductance of the horizontal deflection coil is equally divided into two halves, the voltage applied to the capacitor is rendered lower than a half of the horizontal deflection voltage. It follows that it is possible to shorten the insulating distance for the wiring of the capacitor so as to avoid the enlargement of the wiring substrate and, thus, to lower the manufacturing cost.
Further, according to the cathode ray tube apparatus of the present invention, a resistor is connected in series to the capacitor. Even in the case, the potential difference between the second and third terminals is smaller than that in the conventional case, with the result that it is possible to lower the current flowing into the resistor even if the capacitor is short-circuited, thereby improving the safety.
Further, the similar effect can be obtained even in the case where the third terminal of each of the horizontal deflection coils is formed on the side of the second axis, compared with the distribution angle xcex8 at the edge on the side of the first axis of the winding distribution of the vertical deflection coil.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly point out hereinafter.